EVOH resin compositions are superior in gas barrier properties. Thus, the EVOH resin compositions have been molded into films, sheets, containers, etc. and widely used as various types of packaging materials, etc. For example, an EVOH film constitutes a laminate together with a thermoplastic resin film superior in moisture resistance, mechanical characteristics, etc., especially a film of polyolefin-derived resin, leading to use in a variety of fields as a packaging material. Such a packaging material has been widely used as a container superior in, e.g., oxygen barrier properties, in the form of a bag, a tube, a cup, a pouch or the like in fields including foods, cosmetics, medical drugs, chemicals, toiletries, and vacuum thermal insulated panels. In addition, such a packaging material has also been used in fields in which barrier properties against evaporated gasoline are required, such as gasoline tanks of automobiles. EVOH resin compositions for use in packaging materials in these fields are required to satisfy various characteristics as in the following.
The aforementioned EVOH resin compositions are required to exhibit superior appearance characteristics also after melt molding, e.g., the absence of yellow coloration on the end face of a roll obtained after winding the EVOH resin compositions in the form of a roll in a film molding step.
Moreover, the EVOH resin compositions are also required to achieve a reduction of a break of a film which may occur due to tension between rolls in a film-unwinding step or the like in laminating other thermoplastic resin layer on the EVOH film and/or forming a vapor deposition layer (i.e., film-breaking resistance), and to exhibit superior slidability between films in the case of their storage in the form of a film roll, and between a roll used in the production step and the EVOH film in their lamination processing (i.e., blocking resistance).
Furthermore, since vapor deposition defects such as pinholes generated in vapor deposition processing lead to deterioration of gas barrier performances (see Japanese Unexamined Patent Application, Publication No. 2005-290108), the inhibition of the generation of the vapor deposition defects and a time-dependent increase of the defects in the vapor deposition processing is required.
Moreover, in laminates including a vapor deposition layer, an increase of adhesive strength between the vapor deposition layer and the EVOH film, and the inhibition of delamination and the like which may cause unfavorable appearances are also required.
In order to address these requirements, a method has been proposed in which an acid such as carboxylic acid and phosphoric acid, and a metal salt such as an alkali metal salt and an alkaline earth metal are incorporated in an appropriate amount to prevent the occurrence of coloring such as yellowing in the melt molding (see Japanese Unexamined Patent Application, Publication No. 2001-146539). Alternatively, the incorporation of an oxide and a boron compound has been proposed to improve the slidability and the blocking resistance of a film (see Japanese Unexamined Patent Application, Publication No. 2000-265024). Furthermore, in order to inhibit the deterioration of the gas barrier performances due to pinholes generated in the vapor deposition processing, it has been proposed to use a multilayered structure including at least one layer obtained by subjecting a resin film for a surface treatment, which has a molar ratio of an oxygen atom to a carbon atom on the film surface of 0.24 or greater, to a treatment with aluminum metal or silicon oxide (see Japanese Unexamined Patent Application, Publication No. 2005-290108).
However, the method in which the acid and the metal salt are incorporated in an appropriate amount, which is disclosed in Japanese Unexamined Patent Application, Publication No. 2001-146539 described above cannot sufficiently inhibit the occurrence of coloring such as yellowing in the melt molding. Moreover, although the incorporation of the oxide and the boron compound as disclosed in Japanese Unexamined Patent Application, Publication No. 2000-265024 described above improves the slidability and the blocking resistance of the film, the inhibition of the generation of the pinholes in the vapor deposition processing and the lamination processability are unsatisfactory. Furthermore, in the multilayered structure disclosed in Japanese Unexamined Patent Application, Publication No. 2005-290108 described above, since the generation of the pinholes in the layer subjected to the treatment with the aluminum metal or silicon oxide has not been reduced, the deterioration of the barrier properties is concerned. Thus, the conventional resin compositions cannot satisfy the aforementioned requirements. In addition, an attention should be paid to an odor in molding from an environmental viewpoint.